As electronic and electric technologies develop rapidly, high power, high efficiency, and high power density have become a development trend of a switching power supply. As one type of the switching power supply, a resonant converter is widely applied in the industry due to advantages such as high efficiency and high power density. The resonant converter has a synchronous rectification circuit, to enhance output efficiency of the resonant converter. Currently, control on the on-off state of the synchronous rectification circuit refers to a controller that samples voltages at two ends of each rectification switch component in the synchronous rectification circuit and controls the on-off state of each switch component according to a result of sampling. Because each switch component has inductance, a result of voltage sampling is incorrect, so that the on-off state of each rectification switch component cannot be precisely controlled.